Australopithecus afarensis, the early human who lived about 3.2 million years ago, walked upright, according to an "evolutionary robotics" model.

The model, which uses footprints to predict gait, suggests "Lucy", as the first fossil afarensis was called, walked rather like us.

This contradicts earlier suggestions that Lucy shuffled like a bipedally walking chimpanzee.

The research is published in the Royal Society Interface journal.

"I think it is very interesting work," Professor Chris Stringer, head of human origins at the Natural History Museum in London, told the BBC News website. "There was controversy as to whether [footprints purported to be from afarensis] were showing a human pattern. And it looks like they do."

How human?

Lucy was discovered in Ethiopia in 1974, by a team of palaeoanthropologists who were fans of the Beatles' song Lucy in the Sky with Diamonds.

It doesn't end the argument because there is still the possibility that there were different creatures around at the time

Prof Chris Stringer, Natural History Museum

The ancient hominid had many features reminiscent of her early ape ancestry, but she also carried hints of her future descendents.

Her jaw was protruding and her forehead sloped back. But she seemed human, too; her posture being more upright than that of a chimpanzee.

However, there has been a debate about how "human" Lucy's posture actually was.

Some scientists maintain she was probably rather stooped and may have shuffled awkwardly, much like a modern chimp does when it is walking bipedally for short distances; while others think she was upright, routinely walking tall on two legs.

Twenty-five years ago, some footprints were found in Laetoli, Tanzania. The lonely path, trodden by at least two individuals walking side by side, was preserved immaculately in volcanic ash. It is thought to have been left by a pair of Australopithecus afarensis, vainly retreating from an erupting volcano.

The discovery of the Laetoli footprints generated a flurry of interest in scientists hoping to clear up the "posture debate".

Some felt the prints suggested a human-like gait but others were not convinced.

Questions remain

Now, a team of scientists from around the UK have used computer robotic techniques to work out the most energy efficient gait for afarensis based on Lucy's skeleton and the Laetoli footprint trails.

They claim to have cleared up the debate by finding that, based on their model, Lucy almost certainly did walk tall.

There has been a long-standing debate about how human Lucy was

"Assuming that the early human relative Australopithecus afarensis was the maker of the Laetoli footprint trails, our study suggests that by 3.5 million years ago at least some of our early relatives - despite their small stature - could sustain efficient bipedal walking at absolute speeds within the range shown by modern humans," co-author Weijie Wang, from Dundee University, told the Scotsman newspaper.

However, Professor Stringer believes the controversy will not vanish overnight.

"There are still some people who argue that, looking at the anatomy of the foot bones of afarensis, that they were unlikely to have made the Laetoli footprints," he told the BBC News website.

"So it doesn't end the argument because there is still the possibility that there were different creatures around at the time."